Our invention is in the general area of orthopedic prostheses, particularly, artificial knees. Specifically, our invention relates to a femoral component of an artificial knee prosthesis which can be used with or without a posterior stabilized feature.
The two largest and longest bones of the human body, femur and the tibia, meet at a person's knee. The tibia is situated at the front and inner side of the lower leg. It is prismoid in form, and expanded above where it enters into the knee joint. At the top of the tibia are two smooth compartments or surfaces which articulate with the condyles of the femur. Posteriorly, the condyles and compartments are separated from each other by a shallow depression for the attachment of ligaments. Because the knee has great mobility in flexion, it relies on a set of ligaments to constrain its motion when bent. These include the medial and lateral collateral ligaments and the posterior and anterior cruciate ligaments.
Because of wear and tear or disease, the articulating surfaces of the knee may degrade. To treat certain pathologies, it has become common to surgically remove either the condyles or the compartments or both and replace these structures with prosthetic implants. To preserve the ligaments around the knee, it is desirable to remove as little of the bone structure as possible. However, conditions may dictate that a larger amount of the bone structure be removed in the first instance, or the degradation of bone or ligaments may continue after the initial implants, requiring a revision or second operation wherein more bone is removed and a more robust prosthesis is installed. In these situations, the attachments sites of the constraining ligaments may also of necessity be removed. In these situations, the constraining action of the ligaments must be replaced by another mechanism.
Such a mechanism is known in the art as a posterior stabilized prosthetic knee. These structures typically have an eminence in the center of an articulating surface of the tibial component which mates with pronounced cross member in the femoral component. They are constrained from tibial posterior translation by the posterior wall of this tibial prominence engaging femoral cross member. Such a prosthesis is known from U.S. Pat. No. 4,213,299 to Insall.
When a revision operation is necessary, it is sometimes desirable to add a posterior stabilized feature because the posterior cruciate ligament has continued to degenerate, although the femoral surfaces have not. It has been suggested by Hofmann, U.S. Pat. No. 5,116,375, that a removable stabilizing rod or pin should be provided in the femoral component which can be added during the revision operation without removing the femoral prosthesis.